Biochemical studies on composting of municipal sewage sludge mixed with rice hull

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Abstract
A mixture of undigested sewage sludge cake with rice hull was composted and the changes in various biological and biochemical properties of the mixture were investigated in the process of composting. The salient features obtained were as follows: 1) The contents of T-C, T-N, and various carbon and nitrogen compounds did not show any significant variation during composting, although a slight decrease in the contents of acid hydrolyzable nitrogen compounds was detected at the initial stage of the composting (active composting). 2) Cellulase activity was low during active composting and increased after 23 days of the composting (curing). 3) Protease activity was low at the initial stage when the generation of NH, was active. 4) Tbe activities of the enzymes were higher when the temperature of the incubation was 60°C than when it was 30°C. 5) Predominant microflora consisted of aerobic bacteria throughout the composting period and no significant increase in the number of actinomycetes was observed when cellulase activity increased. 6) The decomposition of the filter paper buried in the pile of the compost started on the 23rd day of the composting when the cellulase activity increased. 7) Electron microscopic observation of rice hull revealed that its decomposition was almost completed in the period between 60–80 days after the initiation of the composting.